How to check if a string contains a substring in Bash

Question

I have a string in Bash  string  quot My string quot   How can I test if it contains another string  if    string     foo     then   echo  quot It s there  quot  fi  Where    is my unknown operator  Do I use echo and grep  if echo  quot  string quot    grep  foo   then   echo  quot It s there  quot  fi  That looks a bit clumsy

User · Answer

I found to need this functionality quite frequently, so I'm using a home-made shell function in my .bashrc like this which allows me to reuse it as often as I need to, with an easy to remember name:

function stringinstring()
{
    case "$2" in
       *"$1"*)
          return 0
       ;;
    esac
    return 1
}

To test if $string1 (say, abc) is contained in $string2 (say, 123abcABC) I just need to run stringinstring "$string1" "$string2" and check for the return value, for example

stringinstring "$str1" "$str2"  &&  echo YES  ||  echo NO

User · Answer

Exact word match   string  My long string  exactSearch  long   if grep -E -q   b  exactSearch  b   lt  lt  lt   string   gt  dev null 2 gt  amp 1   then     echo  It s there    fi

User · Answer

stringContain variants  compatible or case independent   As these Stack Overflow answers tell mostly about Bash  I ve posted a case independent Bash function at the very bottom of this post     Anyway  there is my  Compatible answer  As there are already a lot of answers using Bash-specific features  there is a way working under poorer-featured shells  like BusyBox     -z    string    reqsubstr        In practice  this could give   string  echo  My string   for reqsubstr in  o  M   alt   str  do   if   -z    string    reqsubstr       then       echo  String   string  contain substring    reqsubstr        else       echo  String   string  don t contain substring    reqsubstr        fi   done   This was tested under Bash  Dash  KornShell  ksh  and ash  BusyBox   and the result is always   String  echo  My string   contain substring   o  M   String  echo  My string   don t contain substring   alt   String  echo  My string   contain substring   str     Into one function  As asked by  EeroAaltonen here is a version of the same demo  tested under the same shells   myfunc         reqsubstr   1      shift     string          if   -z    string    reqsubstr       then         echo  String   string  contain substring    reqsubstr           else         echo  String   string  don t contain substring    reqsubstr        fi     Then     myfunc  o  M   echo  My String   String  echo  My String   contain substring  o  M      myfunc  alt   echo  My String   String  echo  My String   don t contain substring  alt     Notice  you have to escape or double enclose quotes and or double quotes     myfunc  o  M  echo  My String  String  echo My String  don t contain substring   o  M      myfunc  o  M  echo   My String   String  echo  My String   contain substring   o  M     Simple function  This was tested under BusyBox  Dash  and  of course Bash   stringContain       -z    2    1           Then now     if stringContain  o  M3   echo  My String   then echo yes else echo no fi no   if stringContain  o  M   echo  My String   then echo yes else echo no fi yes       Or if the submitted string could be empty  as pointed out by  Sjlver  the function would become   stringContain       -z    2    1       amp  amp    -z   1  -o -n   2         or as suggested by Adrian G  nter s comment  avoiding -o switches     stringContain       -z    2    1       amp  amp      -z   1         -n   2            Final  simple  function   And inverting the tests to make them potentially quicker   stringContain       -z   1           -z    2    1       amp  amp    -n   2          With empty strings     if stringContain        then echo yes  else echo no  fi yes   if stringContain  o  M      then echo yes  else echo no  fi no   Case independent  Bash only    For testing strings without care of case  simply convert each string to lower case   stringContain         local  lc   2          -z   1           -z     lc     1          amp  amp    -n   2            Check   stringContain  o  M3   echo  my string    amp  amp  echo yes    echo no no stringContain  o  My   echo  my string    amp  amp  echo yes    echo no yes if stringContain        then echo yes  else echo no  fi yes if stringContain  o  M      then echo yes  else echo no  fi no

User · Answer

I use this function  one dependency not included but obvious   It passes the tests shown below  If the function returns a value   0 then the string was found  You could just as easily return 1 or 0 instead   function str instr        Return position of    str    within    string           gt  gt  gt  str instr  str   string       str  String to search for       string  String to search     typeset str string x      Behavior here is not the same in bash vs ksh unless we escape special characters     str    str escape special characters    1        string    2      x    string   str       if       x         string       then       echo     x    1    bc -l    else       echo 0    fi    function test str instr      str instr       foo host  dev web      assert eq 11    str instr       foo host  dev web      assert eq 19    str instr       foo host  dev web      assert eq 11    str instr       foo host  dev web      assert eq 19    str instr  a   abc    assert eq 1    str instr  z   abc    assert eq 0    str instr  Eggs   Green Eggs And Ham    assert eq 7    str instr  a       assert eq 0    str instr         assert eq 0    str instr      Green Eggs    assert eq 6    str instr       Green      assert eq 1

User · Answer

Extension of the question answered here How do you tell if a string contains another string in POSIX sh    This solution works with special characters     contains string  substring      Returns 0 if the specified string contains the specified substring    otherwise returns 1  contains         string   1      substring   2       if echo   string      type -p ggrep grep   head -1  -F --   substring   gt  dev null  then         return 0       substring is in  string     else         return 1       substring is not in  string     fi    contains  abcd   e     echo  abcd does not contain e  contains  abcd   ab   amp  amp  echo  abcd contains ab  contains  abcd   bc   amp  amp  echo  abcd contains bc  contains  abcd   cd   amp  amp  echo  abcd contains cd  contains  abcd   abcd   amp  amp  echo  abcd contains abcd  contains        amp  amp  echo  empty string contains empty string  contains  a      amp  amp  echo  a contains empty string  contains     a     echo  empty string does not contain a  contains  abcd efgh   cd ef   amp  amp  echo  abcd efgh contains cd ef  contains  abcd efgh       amp  amp  echo  abcd efgh contains a space   contains  abcd  efg  hij    efg    amp  amp  echo  abcd  efg  hij contains  efg   contains  abcd  efg  hij    effg      echo  abcd  efg  hij does not contain  effg    contains  abcd  efg  hij    efg    amp  amp  echo  abcd  efg  hij contains  efg   contains  abcd  efg  hij   d  efg  h   amp  amp  echo  abcd  efg  hij contains d  efg  h  contains  abcd  efg  hij    effg      echo  abcd  efg  hij does not contain  effg

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msg  message   function check       echo  msg   egrep  abc  1 gt   dev null      if      -ne 1        then          echo  found       else          echo  not found       fi    check   This will find any occurance of a or b or c

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You can use Marcus s answer    wildcards  outside a case statement  too  if you use double brackets   string  My long string  if     string      My long       then   echo  It s there   fi   Note that spaces in the needle string need to be placed between double quotes  and the   wildcards should be outside  Also note that a simple comparison operator is used  i e       not the regex operator

User · Answer

If you prefer the regex approach  string  My string    if     string     quot My quot      then    echo  quot It s there  quot  fi

User · Answer

grep -q is useful for this purpose   The same using awk   string  unix-bash 2389  character     printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Not Found     string  unix-bash 2389  character  -  printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Found   Original source  http   unstableme blogspot com 2008 06 bash-search-letter-in-string-awk html

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I am not sure about using an if statement  but you can get a similar effect with a case statement   case   string  in     foo         Do stuff        esac

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string     foo      amp  amp  echo  It s there     echo  Couldn t find

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The accepted answer is best  but since there s more than one way to do it  here s another solution   if     string        string foo       then     echo  It s there   fi     var search replace  is  var with the first instance of search replaced by replace  if it is found  it doesn t change  var    If you try to replace foo by nothing  and the string has changed  then obviously foo was found

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One is       expr  mystring        search      -ne 0    amp  amp  echo  yes      echo  no

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You can use Marcus s answer    wildcards  outside a case statement  too  if you use double brackets   string  My long string  if     string      My long       then   echo  It s there   fi   Note that spaces in the needle string need to be placed between double quotes  and the   wildcards should be outside  Also note that a simple comparison operator is used  i e       not the regex operator

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Bash 4  examples  Note  not using quotes will cause issues when words contain spaces  etc  Always quote in Bash  IMO   Here are some examples Bash 4    Example 1  check for  yes  in string  case insensitive        if       str          yes       then   Example 2  check for  yes  in string  case insensitive        if       echo   str    tr    upper       lower           yes       then   Example 3  check for  yes  in string  case sensitive         if       str        yes       then   Example 4  check for  yes  in string  case sensitive         if       str       yes      then   Example 5  exact match  case sensitive         if       str       yes      then   Example 6  exact match  case insensitive         if       str         yes      then   Example 7  exact match        if     a      b     then   Example 8  wildcard match  ext  case insensitive         if echo   a    egrep -iq     mp 3-4  txt css jpg png     then   Enjoy

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If you prefer the regex approach  string  My string    if     string     quot My quot      then    echo  quot It s there  quot  fi

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Try oobash   It is an OO-style string library for Bash 4  It has support for German umlauts  It is written in Bash   Many functions are available  -base64Decode  -base64Encode  -capitalize  -center  -charAt  -concat  -contains  -count  -endsWith  -equals  -equalsIgnoreCase  -reverse  -hashCode  -indexOf  -isAlnum  -isAlpha  -isAscii  -isDigit  -isEmpty  -isHexDigit  -isLowerCase  -isSpace  -isPrintable  -isUpperCase  -isVisible  -lastIndexOf  -length  -matches  -replaceAll  -replaceFirst  -startsWith  -substring  -swapCase  -toLowerCase  -toString  -toUpperCase  -trim  and -zfill   Look at the contains example    Desktop   String a testXccc  Desktop   a contains tX true  Desktop   a contains XtX false   oobash is available at Sourceforge net

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Try oobash   It is an OO-style string library for Bash 4  It has support for German umlauts  It is written in Bash   Many functions are available  -base64Decode  -base64Encode  -capitalize  -center  -charAt  -concat  -contains  -count  -endsWith  -equals  -equalsIgnoreCase  -reverse  -hashCode  -indexOf  -isAlnum  -isAlpha  -isAscii  -isDigit  -isEmpty  -isHexDigit  -isLowerCase  -isSpace  -isPrintable  -isUpperCase  -isVisible  -lastIndexOf  -length  -matches  -replaceAll  -replaceFirst  -startsWith  -substring  -swapCase  -toLowerCase  -toString  -toUpperCase  -trim  and -zfill   Look at the contains example    Desktop   String a testXccc  Desktop   a contains tX true  Desktop   a contains XtX false   oobash is available at Sourceforge net

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So there are lots of useful solutions to the question - but which is fastest   uses the fewest resources   Repeated tests using this frame    usr bin time bash -c  a two b onetwothree  x 100000  while    x -gt 0    do TEST   x     x-1    done    Replacing TEST each time       b     a              2 92 user 0 06 system 0 02 99 elapsed 99  CPU       b  a         b      3 16 user 0 07 system 0 03 25 elapsed 99  CPU      b      a             1 85 user 0 04 system 0 01 90 elapsed 99  CPU  case  b in   a    esac   1 80 user 0 02 system 0 01 83 elapsed 99  CPU  doContain  a  b          4 27 user 0 11 system 0 04 41 elapsed 99 CPU    doContain was in F  Houri s answer   And for giggles   echo  b grep -q  a       12 68 user 30 86 system 3 42 40 elapsed 19  CPU  ouch    So the simple substitution option predictably wins whether in an extended test or a case  The case is portable   Piping out to 100000 greps is predictably painful  The old rule about using external utilities without need holds true

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One is       expr  mystring        search      -ne 0    amp  amp  echo  yes      echo  no

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So there are lots of useful solutions to the question - but which is fastest   uses the fewest resources   Repeated tests using this frame    usr bin time bash -c  a two b onetwothree  x 100000  while    x -gt 0    do TEST   x     x-1    done    Replacing TEST each time       b     a              2 92 user 0 06 system 0 02 99 elapsed 99  CPU       b  a         b      3 16 user 0 07 system 0 03 25 elapsed 99  CPU      b      a             1 85 user 0 04 system 0 01 90 elapsed 99  CPU  case  b in   a    esac   1 80 user 0 02 system 0 01 83 elapsed 99  CPU  doContain  a  b          4 27 user 0 11 system 0 04 41 elapsed 99 CPU    doContain was in F  Houri s answer   And for giggles   echo  b grep -q  a       12 68 user 30 86 system 3 42 40 elapsed 19  CPU  ouch    So the simple substitution option predictably wins whether in an extended test or a case  The case is portable   Piping out to 100000 greps is predictably painful  The old rule about using external utilities without need holds true

User · Answer

My  bash profile file and how I used grep   If the PATH environment variable includes my two bin directories  don t append them      bash profile   Get the aliases and functions if   -f    bashrc    then          bashrc fi  U    local bin   bin  if   echo   PATH    grep -q  home   then     export PATH  PATH   U  fi

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Bash 4  examples  Note  not using quotes will cause issues when words contain spaces  etc  Always quote in Bash  IMO   Here are some examples Bash 4    Example 1  check for  yes  in string  case insensitive        if       str          yes       then   Example 2  check for  yes  in string  case insensitive        if       echo   str    tr    upper       lower           yes       then   Example 3  check for  yes  in string  case sensitive         if       str        yes       then   Example 4  check for  yes  in string  case sensitive         if       str       yes      then   Example 5  exact match  case sensitive         if       str       yes      then   Example 6  exact match  case insensitive         if       str         yes      then   Example 7  exact match        if     a      b     then   Example 8  wildcard match  ext  case insensitive         if echo   a    egrep -iq     mp 3-4  txt css jpg png     then   Enjoy

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stringContain variants  compatible or case independent   As these Stack Overflow answers tell mostly about Bash  I ve posted a case independent Bash function at the very bottom of this post     Anyway  there is my  Compatible answer  As there are already a lot of answers using Bash-specific features  there is a way working under poorer-featured shells  like BusyBox     -z    string    reqsubstr        In practice  this could give   string  echo  My string   for reqsubstr in  o  M   alt   str  do   if   -z    string    reqsubstr       then       echo  String   string  contain substring    reqsubstr        else       echo  String   string  don t contain substring    reqsubstr        fi   done   This was tested under Bash  Dash  KornShell  ksh  and ash  BusyBox   and the result is always   String  echo  My string   contain substring   o  M   String  echo  My string   don t contain substring   alt   String  echo  My string   contain substring   str     Into one function  As asked by  EeroAaltonen here is a version of the same demo  tested under the same shells   myfunc         reqsubstr   1      shift     string          if   -z    string    reqsubstr       then         echo  String   string  contain substring    reqsubstr           else         echo  String   string  don t contain substring    reqsubstr        fi     Then     myfunc  o  M   echo  My String   String  echo  My String   contain substring  o  M      myfunc  alt   echo  My String   String  echo  My String   don t contain substring  alt     Notice  you have to escape or double enclose quotes and or double quotes     myfunc  o  M  echo  My String  String  echo My String  don t contain substring   o  M      myfunc  o  M  echo   My String   String  echo  My String   contain substring   o  M     Simple function  This was tested under BusyBox  Dash  and  of course Bash   stringContain       -z    2    1           Then now     if stringContain  o  M3   echo  My String   then echo yes else echo no fi no   if stringContain  o  M   echo  My String   then echo yes else echo no fi yes       Or if the submitted string could be empty  as pointed out by  Sjlver  the function would become   stringContain       -z    2    1       amp  amp    -z   1  -o -n   2         or as suggested by Adrian G  nter s comment  avoiding -o switches     stringContain       -z    2    1       amp  amp      -z   1         -n   2            Final  simple  function   And inverting the tests to make them potentially quicker   stringContain       -z   1           -z    2    1       amp  amp    -n   2          With empty strings     if stringContain        then echo yes  else echo no  fi yes   if stringContain  o  M      then echo yes  else echo no  fi no   Case independent  Bash only    For testing strings without care of case  simply convert each string to lower case   stringContain         local  lc   2          -z   1           -z     lc     1          amp  amp    -n   2            Check   stringContain  o  M3   echo  my string    amp  amp  echo yes    echo no no stringContain  o  My   echo  my string    amp  amp  echo yes    echo no yes if stringContain        then echo yes  else echo no  fi yes if stringContain  o  M      then echo yes  else echo no  fi no

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You should remember that shell scripting is less of a language and more of a collection of commands  Instinctively you think that this  language  requires you to follow an if with a   or a     Both of those are just commands that return an exit status indicating success or failure  just like every other command   For that reason I d use grep  and not the   command   Just do   if grep -q foo  lt  lt  lt   string   then     echo  It s there  fi   Now that you are thinking of if as testing the exit status of the command that follows it  complete with semi-colon   why not reconsider the source of the string you are testing      Instead of this filetype    file -b   1    if grep -q  tar archive   lt  lt  lt   filetype   then          Simply do this if file -b   1    grep -q  tar archive   then        The -q option makes grep not output anything  as we only want the return code   lt  lt  lt  makes the shell expand the next word and use it as the input to the command  a one-line version of the  lt  lt  here document  I m not sure whether this is standard or a Bashism

User · Answer

I found to need this functionality quite frequently, so I'm using a home-made shell function in my .bashrc like this which allows me to reuse it as often as I need to, with an easy to remember name:

function stringinstring()
{
    case "$2" in
       *"$1"*)
          return 0
       ;;
    esac
    return 1
}

To test if $string1 (say, abc) is contained in $string2 (say, 123abcABC) I just need to run stringinstring "$string1" "$string2" and check for the return value, for example

stringinstring "$str1" "$str2"  &&  echo YES  ||  echo NO

User · Answer

If you prefer the regex approach  string  My string    if     string     quot My quot      then    echo  quot It s there  quot  fi

User · Answer

You can use Marcus s answer    wildcards  outside a case statement  too  if you use double brackets   string  My long string  if     string      My long       then   echo  It s there   fi   Note that spaces in the needle string need to be placed between double quotes  and the   wildcards should be outside  Also note that a simple comparison operator is used  i e       not the regex operator

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I like sed   substr  foo  nonsub    echo   string    sed  s  substr      hassub 0       string       nonsub     amp  amp  hassub 1   Edit  Logic    Use sed to remove instance of substring from string If new string differs from old string  substring exists

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string     foo      amp  amp  echo  It s there     echo  Couldn t find

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I am not sure about using an if statement  but you can get a similar effect with a case statement   case   string  in     foo         Do stuff        esac

User · Answer

You should remember that shell scripting is less of a language and more of a collection of commands  Instinctively you think that this  language  requires you to follow an if with a   or a     Both of those are just commands that return an exit status indicating success or failure  just like every other command   For that reason I d use grep  and not the   command   Just do   if grep -q foo  lt  lt  lt   string   then     echo  It s there  fi   Now that you are thinking of if as testing the exit status of the command that follows it  complete with semi-colon   why not reconsider the source of the string you are testing      Instead of this filetype    file -b   1    if grep -q  tar archive   lt  lt  lt   filetype   then          Simply do this if file -b   1    grep -q  tar archive   then        The -q option makes grep not output anything  as we only want the return code   lt  lt  lt  makes the shell expand the next word and use it as the input to the command  a one-line version of the  lt  lt  here document  I m not sure whether this is standard or a Bashism

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I use this function  one dependency not included but obvious   It passes the tests shown below  If the function returns a value   0 then the string was found  You could just as easily return 1 or 0 instead   function str instr        Return position of    str    within    string           gt  gt  gt  str instr  str   string       str  String to search for       string  String to search     typeset str string x      Behavior here is not the same in bash vs ksh unless we escape special characters     str    str escape special characters    1        string    2      x    string   str       if       x         string       then       echo     x    1    bc -l    else       echo 0    fi    function test str instr      str instr       foo host  dev web      assert eq 11    str instr       foo host  dev web      assert eq 19    str instr       foo host  dev web      assert eq 11    str instr       foo host  dev web      assert eq 19    str instr  a   abc    assert eq 1    str instr  z   abc    assert eq 0    str instr  Eggs   Green Eggs And Ham    assert eq 7    str instr  a       assert eq 0    str instr         assert eq 0    str instr      Green Eggs    assert eq 6    str instr       Green      assert eq 1

User · Answer

grep -q is useful for this purpose   The same using awk   string  unix-bash 2389  character     printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Not Found     string  unix-bash 2389  character  -  printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Found   Original source  http   unstableme blogspot com 2008 06 bash-search-letter-in-string-awk html

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As Paul mentioned in his performance comparison   if echo  abcdefg    grep -q  bcdef   then     echo  String contains is true   else     echo  String contains is not true   fi   This is POSIX compliant like the  case   string  in  the answer provided by Marcus  but it is slightly easier to read than the case statement answer  Also note that this will be much much slower than using a case statement  As Paul pointed out  don t use it in a loop

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If you prefer the regex approach  string  My string    if     string     quot My quot      then    echo  quot It s there  quot  fi

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This Stack nbsp Overflow answer was the only one to trap space and dash characters     For null cmd arguments checking    to check   -t  space n dash chars   -      to check       space n dash chars       amp  amp  echo found

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Extension of the question answered here How do you tell if a string contains another string in POSIX sh    This solution works with special characters     contains string  substring      Returns 0 if the specified string contains the specified substring    otherwise returns 1  contains         string   1      substring   2       if echo   string      type -p ggrep grep   head -1  -F --   substring   gt  dev null  then         return 0       substring is in  string     else         return 1       substring is not in  string     fi    contains  abcd   e     echo  abcd does not contain e  contains  abcd   ab   amp  amp  echo  abcd contains ab  contains  abcd   bc   amp  amp  echo  abcd contains bc  contains  abcd   cd   amp  amp  echo  abcd contains cd  contains  abcd   abcd   amp  amp  echo  abcd contains abcd  contains        amp  amp  echo  empty string contains empty string  contains  a      amp  amp  echo  a contains empty string  contains     a     echo  empty string does not contain a  contains  abcd efgh   cd ef   amp  amp  echo  abcd efgh contains cd ef  contains  abcd efgh       amp  amp  echo  abcd efgh contains a space   contains  abcd  efg  hij    efg    amp  amp  echo  abcd  efg  hij contains  efg   contains  abcd  efg  hij    effg      echo  abcd  efg  hij does not contain  effg    contains  abcd  efg  hij    efg    amp  amp  echo  abcd  efg  hij contains  efg   contains  abcd  efg  hij   d  efg  h   amp  amp  echo  abcd  efg  hij contains d  efg  h  contains  abcd  efg  hij    effg      echo  abcd  efg  hij does not contain  effg

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case  string in   foo       Do stuff esac   This is the same answer as https   stackoverflow com a 229585 11267590  But simple style and also POSIX Compliant

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This Stack nbsp Overflow answer was the only one to trap space and dash characters     For null cmd arguments checking    to check   -t  space n dash chars   -      to check       space n dash chars       amp  amp  echo found

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This also works   if printf --   s    haystack    egrep -q --   needle  then   printf  Found needle in haystack  fi   And the negative test is   if   printf --   s    haystack    egrep -q --   needle  then   echo  Did not find needle in haystack  fi   I suppose this style is a bit more classic -- less dependent upon features of Bash shell   The -- argument is pure POSIX paranoia  used to protected against input strings similar to options  such as --abc or -a   Note  In a tight loop this code will be much slower than using internal Bash shell features  as one  or two  separate processes will be created and connected via pipes

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case  string in   foo       Do stuff esac   This is the same answer as https   stackoverflow com a 229585 11267590  But simple style and also POSIX Compliant

User · Answer

The accepted answer is best  but since there s more than one way to do it  here s another solution   if     string        string foo       then     echo  It s there   fi     var search replace  is  var with the first instance of search replaced by replace  if it is found  it doesn t change  var    If you try to replace foo by nothing  and the string has changed  then obviously foo was found

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How about this   text      lt tag gt bmnmn lt  tag gt     if      text       lt tag gt       then    echo  matched  else    echo  not matched  fi

User · Answer

I am not sure about using an if statement  but you can get a similar effect with a case statement   case   string  in     foo         Do stuff        esac

User · Answer

grep -q is useful for this purpose   The same using awk   string  unix-bash 2389  character     printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Not Found     string  unix-bash 2389  character  -  printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Found   Original source  http   unstableme blogspot com 2008 06 bash-search-letter-in-string-awk html

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My  bash profile file and how I used grep   If the PATH environment variable includes my two bin directories  don t append them      bash profile   Get the aliases and functions if   -f    bashrc    then          bashrc fi  U    local bin   bin  if   echo   PATH    grep -q  home   then     export PATH  PATH   U  fi

User · Answer

The accepted answer is best  but since there s more than one way to do it  here s another solution   if     string        string foo       then     echo  It s there   fi     var search replace  is  var with the first instance of search replaced by replace  if it is found  it doesn t change  var    If you try to replace foo by nothing  and the string has changed  then obviously foo was found

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You should remember that shell scripting is less of a language and more of a collection of commands  Instinctively you think that this  language  requires you to follow an if with a   or a     Both of those are just commands that return an exit status indicating success or failure  just like every other command   For that reason I d use grep  and not the   command   Just do   if grep -q foo  lt  lt  lt   string   then     echo  It s there  fi   Now that you are thinking of if as testing the exit status of the command that follows it  complete with semi-colon   why not reconsider the source of the string you are testing      Instead of this filetype    file -b   1    if grep -q  tar archive   lt  lt  lt   filetype   then          Simply do this if file -b   1    grep -q  tar archive   then        The -q option makes grep not output anything  as we only want the return code   lt  lt  lt  makes the shell expand the next word and use it as the input to the command  a one-line version of the  lt  lt  here document  I m not sure whether this is standard or a Bashism

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How about this   text      lt tag gt bmnmn lt  tag gt     if      text       lt tag gt       then    echo  matched  else    echo  not matched  fi

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You can use Marcus s answer    wildcards  outside a case statement  too  if you use double brackets   string  My long string  if     string      My long       then   echo  It s there   fi   Note that spaces in the needle string need to be placed between double quotes  and the   wildcards should be outside  Also note that a simple comparison operator is used  i e       not the regex operator

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You should remember that shell scripting is less of a language and more of a collection of commands  Instinctively you think that this  language  requires you to follow an if with a   or a     Both of those are just commands that return an exit status indicating success or failure  just like every other command   For that reason I d use grep  and not the   command   Just do   if grep -q foo  lt  lt  lt   string   then     echo  It s there  fi   Now that you are thinking of if as testing the exit status of the command that follows it  complete with semi-colon   why not reconsider the source of the string you are testing      Instead of this filetype    file -b   1    if grep -q  tar archive   lt  lt  lt   filetype   then          Simply do this if file -b   1    grep -q  tar archive   then        The -q option makes grep not output anything  as we only want the return code   lt  lt  lt  makes the shell expand the next word and use it as the input to the command  a one-line version of the  lt  lt  here document  I m not sure whether this is standard or a Bashism

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I like sed   substr  foo  nonsub    echo   string    sed  s  substr      hassub 0       string       nonsub     amp  amp  hassub 1   Edit  Logic    Use sed to remove instance of substring from string If new string differs from old string  substring exists

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As Paul mentioned in his performance comparison   if echo  abcdefg    grep -q  bcdef   then     echo  String contains is true   else     echo  String contains is not true   fi   This is POSIX compliant like the  case   string  in  the answer provided by Marcus  but it is slightly easier to read than the case statement answer  Also note that this will be much much slower than using a case statement  As Paul pointed out  don t use it in a loop

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Since the POSIX BusyBox question is closed without providing the right answer  IMHO   I ll post an answer here   The shortest possible answer is        string      substring         echo Substring found    or        string      substring          echo  Substring found     Note that the double hash is obligatory with some shells  ash   Above will evaluate   stringvalue   when the substring is not found  It returns no error  When the substring is found the result is empty and it evaluates       This will throw error code 1 since the string is completely substituted  due to      The shortest more common syntax     -z     string      substring        amp  amp  echo  Substring found     or    -n     string      substring          echo  Substring found     Another one         string     substring          string      amp  amp  echo  Substring found     or        string     substring         string        echo  Substring found     Note the single equal sign

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grep -q is useful for this purpose   The same using awk   string  unix-bash 2389  character     printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Not Found     string  unix-bash 2389  character  -  printf   s    string    awk -vc   character     if  gsub c         print  Found    else   print  Not Found         Output      Found   Original source  http   unstableme blogspot com 2008 06 bash-search-letter-in-string-awk html

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msg  message   function check       echo  msg   egrep  abc  1 gt   dev null      if      -ne 1        then          echo  found       else          echo  not found       fi    check   This will find any occurance of a or b or c

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The generic needle haystack example is following with variables     bin bash  needle  a needle  haystack  a needle another needle a third needle  if     haystack       needle       then     echo  needle found  else     echo  needle NOT found  fi

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The generic needle haystack example is following with variables     bin bash  needle  a needle  haystack  a needle another needle a third needle  if     haystack       needle       then     echo  needle found  else     echo  needle NOT found  fi

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Since the POSIX BusyBox question is closed without providing the right answer  IMHO   I ll post an answer here   The shortest possible answer is        string      substring         echo Substring found    or        string      substring          echo  Substring found     Note that the double hash is obligatory with some shells  ash   Above will evaluate   stringvalue   when the substring is not found  It returns no error  When the substring is found the result is empty and it evaluates       This will throw error code 1 since the string is completely substituted  due to      The shortest more common syntax     -z     string      substring        amp  amp  echo  Substring found     or    -n     string      substring          echo  Substring found     Another one         string     substring          string      amp  amp  echo  Substring found     or        string     substring         string        echo  Substring found     Note the single equal sign

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Exact word match   string  My long string  exactSearch  long   if grep -E -q   b  exactSearch  b   lt  lt  lt   string   gt  dev null 2 gt  amp 1   then     echo  It s there    fi

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The accepted answer is best  but since there s more than one way to do it  here s another solution   if     string        string foo       then     echo  It s there   fi     var search replace  is  var with the first instance of search replaced by replace  if it is found  it doesn t change  var    If you try to replace foo by nothing  and the string has changed  then obviously foo was found

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This also works   if printf --   s    haystack    egrep -q --   needle  then   printf  Found needle in haystack  fi   And the negative test is   if   printf --   s    haystack    egrep -q --   needle  then   echo  Did not find needle in haystack  fi   I suppose this style is a bit more classic -- less dependent upon features of Bash shell   The -- argument is pure POSIX paranoia  used to protected against input strings similar to options  such as --abc or -a   Note  In a tight loop this code will be much slower than using internal Bash shell features  as one  or two  separate processes will be created and connected via pipes

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I am not sure about using an if statement  but you can get a similar effect with a case statement   case   string  in     foo         Do stuff        esac

[string] How to check if a string contains a substring in Bash

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